The head of the European commission today launched a strong attack on the German chancellor Angela Merkel's handling of the euro's crisis of confidence.

José Manuel Barroso, the president of the European commission, who is believed to be supported by a majority of the 27 member states, described Merkel's campaign to reopen the Lisbon treaty as "naïve". He said that the bill of almost €900bn for rescuing Greece and shoring up the euro would have been much cheaper had Berlin acted more swiftly, and accused the German government of failing to lead public opinion in defence of thebeleaguered single currency.

Barroso's surprisingly public criticism, in an interview with Germany's conservative newspaper the Frankfurter Allgemeine Zeitung, signalled the high-level political friction in the EU over how to restore faith in the single currency.

Barroso's staff, as well as the governments of many other EU member states, think the mixture of hard line and prevarication shown by Merkel since the crisis erupted in February have made a bad situation worse. They say that swift action in February would have deterred the financial markets and contained the crisis to Greece and its sovereign debt.

Delay and ambivalence have instead triggered a full-blown single currency crisis. Merkel is pushing for a tough new regime for the eurozone, the 16 countries using the currency.

Last Friday, Berlin tabled a nine-point plan including swingeing penalties for euro countries that persist in flouting the rules. Some of the new rules could mean reopening the Lisbon treaty which only came into force last November after eight years of fraught negotiations.

"We won't be tabling any proposals for changing the treaty," Barroso said, describing the quest for Lisbon as "a traumatic experience. It would be naive to think that you can reform the treaty only in the areas important to Germany. Of course, then the British and others would come with their wishes."

David Cameron has in the past promised a referendum in the UK over the Lisbon treaty and would come under intense pressure to redeem that pledge if the treaty was up for re-negotiation.

All of the key points proposed by Berlin were opposed by Barroso. Contradicting Merkel, he said it was not possible to expel chronic sinners from the eurozone, that delinquents should not have to forfeit their EU votes for at least a year, as demanded by Berlin. He also made no mention of Germany's call for debt-crippled countries to be allowed to go insolvent.

Senior commission officials said that many EU countries shared their criticism of Germany, the EU's traditional paymaster which has been deeply reluctant first to bail out Greece and then to agree a €750bn fund to shore up the euro. Commission officials accused Merkel of a "failure of political leadership" and of exploiting domestic political problems to justify inaction.

The single currency crisis has triggered a torrent of aggrieved comment in the German media and complaints that thrifty German taxpayers are having to shell out to subsidise the wastrel habits of southern Europeans.

Barroso countered that Merkel and other German leaders were failing to make the case for the euro at home.

"Perhaps from the start one might have been able to say more clearly that Germany has a strong interest in keeping the euro stable, indeed not just out of European solidarity but in its own interest," said Barroso. "It would have been better if we had been able to take a decision earlier. Outside Europe, from the US to Brazil or Japan, one expected a quicker reaction."

Despite the German rancour, Barroso insisted on Berlin's central responsibility for the single currency as the EU's biggest economy and champion exporter.

"Until now Germany has been one of the big winners from the euro. More politicians in Germany should say that clearly," he said. "By the way, it was not Greece, Ireland or Spain who invented the euro. It was a German-French project."